Experimental study of Interfacial and Sub-Interfacial Quasistatic Crack Growth

由金属、陶瓷和聚合物复合材料制成的多相部件在工业上的重要性推动了双材料和多相材料系统中失效机理的研究。了解这些系统中的故障模式在从先进的复合材料飞机结构到电子设备的封装等各种应用中都是相关的。这类系统的失效可以由多种机制引起：脆性基质的宏观和微观破裂、不同材料之间的界面破裂、分层等，具体取决于材料系统的特性。在NSF之前的一项研究拨款下，PI的研究小组开发了一种紧凑型偏振镜/剪切干涉仪(PSI)，既可以用作偏振镜，也可以用作剪切干涉仪。这种单一的设备允许人们从光学各向异性材料(如同质沸石和环氧树脂)以及基本上光学各向同性材料(如PMMA和玻璃)获得应力状态。通过组合光学各向同性和各向异性模型材料可以提供的材料失配参数范围基本上跨越了通常在具有重要技术意义的双材料系统中获得的范围，因此来自模型材料组合的结果具有广泛的适用性。获得了双材料系统在静载荷作用下裂纹萌生的直接光学数据。在这项工作中，将获得关于准静态扩展界面和亚界面裂纹周围的应力状态的全场光学干涉信息。在这项研究中，以前开发的用于监测裂纹萌生的光学干涉仪将与相对高速的录像机(6000帧/秒)一起用于监测准静态扩展。在光学数据的视频记录的同时，还将使用安装在加载装置上的称重传感器和线性变化的位移传感器来记录加载和加载点位移数据，并且这些将用于数值建模，该数值建模可用于解释实验数据。在双材料和多层夹层试件上进行了一系列的试验。值得特别关注的现象是：*界面裂纹扩展机制，其中裂纹完全在两种不同材料之间的界面上扩展；*裂纹扭结机制，其中裂纹从界面开始，但连接到韧性较低的材料中；*裂纹从界面扭曲并在韧性较低的材料中继续扩展后的界面下裂纹扩展机制；*夹层中的裂纹隧道机制。收集的数据和进行的分析，除了证实界面裂纹萌生和裂纹平行问题的知识现状外，还应该为我们提供更多的信息，以更好地理解裂纹扭结和裂纹隧道现象。

Study of failure mechanisms in bimaterial and multiphase material systems is motivated by the industrial importance of multiphase components made from metals, ceramics and polymer composite materials. An understanding of failure modes in these systems is relevant in applications ranging from advanced composite aircraft structures to packaging of electronic devices. Failure in such systems can be due to a variety of mechanisms: macro- and microcracking of a brittle matrix, cracking along interfaces between dissimilar materials, delaminations and so on depending on the specifics of the material system. Under a prior research grant from the NSF, the PI's research group has developed a compact Polariscope/Shearing Interferometer (PSI) that can be used as either a polariscope or a shearing interferometer. This single device allows one to obtain stress states from optically anisotropic materials (such as Homolite and epoxy) as well as essentially optically isotropic materials (such as PMMA and glass). The range of material mismatch parameters that can be provided by combining optically isotropic and anisotropic model materials essentially spans the range that is typically obtained in technologically important bimaterial systems, consequently results from the model material combinations have wide ranging applicability. Direct optical data regarding crack initiation from statically-loaded bimaterial systems have been obtained. In this work, full-field optical interferometric information will be obtained about the stress state around quasi-statically propagating interfacial and sub-interfacial cracks. The optical interferometers previously developed for monitoring crack initiation will be used in this study in conjunction with a relatively high-speed video recorder (6000 frames/see) to monitor quasi-static propagation. Simultaneous with the video recording of the optical data, load and load-point displacement data will also be recorded using a load cell and a linearly-varying displacement transducer mounted on the loading device, and these will be used in numerical modeling that can be of use in interpreting the experimental data. A series of experiments on bimaterial and multilayer sandwich specimens will be conducted. Phenomena of particular interest are: * the interfacial crack propagation regime where the crack propagates entirely on the interface between two dissimilar materials; * the crack kinking regime where the crack starts from the interface but kinks into the material with lower toughness; * the sub-interfacial crack propagation regime after the crack kinks from the interface and continues in the material with lower toughness; * the crack tunneling mechanisms in sandwiched layers. The data gathered, and the analysis performed, should provide us with additional information to gain a better understanding of crack kinking and crack tunneling phenomena, in addition to substantiating the current state of knowledge of issues of interfacial crack initiation and crack paralleling.